处理XStream不支持属性、值同时出现的缺陷

本文介绍如何通过实现Converter接口来自定义XStream处理带有属性的字段的方式,并提供了一个具体的例子,展示了如何创建并注册一个自定义的AttributeValueConveter。

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XStream在处理<Field name="value">text</Field>的情况无能为力,如果要他支持就要写一个Converter,贴上Converter程序如下:

 

package stream;

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import com.thoughtworks.xstream.converters.Converter;
import com.thoughtworks.xstream.converters.MarshallingContext;
import com.thoughtworks.xstream.converters.UnmarshallingContext;
import com.thoughtworks.xstream.converters.reflection.ObjectAccessException;
import com.thoughtworks.xstream.io.HierarchicalStreamReader;
import com.thoughtworks.xstream.io.HierarchicalStreamWriter;
import com.thoughtworks.xstream.mapper.Mapper;

/**
 * 
 * @author Zhao.Allen
 * 
 */
public class AttributeValueConveter implements Converter {

	public String textName = "value";
	private Mapper mapper;
	private List convertClass = new ArrayList();

	public AttributeValueConveter(Mapper mapper) {
		this.mapper = mapper;
	}

	public void marshal(Object obj, HierarchicalStreamWriter wt, MarshallingContext context) {
		Field[] values = obj.getClass().getDeclaredFields();
		for (int i = 0; i < values.length; i++) {
			Field value = values[i];
			String name = value.getName();
			if (name.equals(textName)) {
				continue;
			}
			try {
				if (!value.isAccessible()) {
					value.setAccessible(true);
				}
				Object v = value.get(obj);
				if (v == null) {
					continue;
				}
				if (Number.class.isAssignableFrom(v.getClass()) || v.getClass().isPrimitive()) {
					wt.addAttribute(mapper.serializedMember(obj.getClass(), name), String.valueOf(v));
				} else {
					wt.addAttribute(mapper.serializedMember(obj.getClass(), name), v.toString());
				}
			} catch (Exception e) {
				throw new ObjectAccessException("Cannot set Field " + value.getName() + obj.getClass(), e);
			}
		}
		try{
			Field field = obj.getClass().getDeclaredField(textName);
			if(!field.isAccessible()){
				field.setAccessible(true);
			}
			Object v = field.get(obj);
			if (null != v && !"".equals(v.toString())) {
				wt.setValue(v.toString());
			}
		} catch (Exception e) {
			throw new ObjectAccessException("Cannot set Field " + textName + obj.getClass(), e);
		}
	}

	public Object unmarshal(HierarchicalStreamReader reader, UnmarshallingContext context) {
		Object obj = context.currentObject();
		if (obj == null) {
			try {
				obj = context.getRequiredType().newInstance();
			} catch (Exception e) {
				throw new ObjectAccessException("Cannot construct " + context.getRequiredType().getName(), e);
			}
		}

		Iterator attNames = reader.getAttributeNames();
		while (attNames.hasNext()) {
			String attName = (String) attNames.next();
			if (attName.equals(textName)) {
				continue;
			}

			try {
				Field field = obj.getClass().getDeclaredField(mapper.realMember(obj.getClass(), attName));
				if (!field.isAccessible()) {
					field.setAccessible(true);
				}
				String v = reader.getAttribute(attName);
				if (null == v || "".equals(v)) {
					continue;
				}
				Class fieldType = field.getType();
				Constructor strnum = fieldType.getDeclaredConstructor(String.class);
				field.set(obj, strnum.newInstance(v));
			} catch (Exception e) {
				e.printStackTrace();
				throw new ObjectAccessException("Cannot construct " + obj.getClass(), e);
			}
		}
		String value = reader.getValue();
		if (null != value && !"".equals(value)) {
			try {
				Field field = obj.getClass().getDeclaredField(mapper.realMember(obj.getClass(), textName));
				if (!field.isAccessible()) {
					field.setAccessible(true);
				}
				field.set(obj, value);
			} catch (Exception e) {
				e.printStackTrace();
				throw new ObjectAccessException("Cannot construct " + obj.getClass(), e);
			}
		}
		return obj;
	}

	public boolean canConvert(Class clazz) {
		/*Iterator it = convertClass.iterator();
		while (it.hasNext()) {
			Class c = (Class) it.next();
			if (c.equals(clazz)) {
				return true;
			}
		}return false;*/
		return convertClass.contains(clazz);
	}

	public Iterator getConvertClass() {
		return convertClass.iterator();
	}

	public void addConvertClass(Class cc) {
		this.convertClass.add(cc);
	}

	public String getTextName() {
		return textName;
	}
	public void setTextName(String textName) {
		this.textName = textName;
	}
}

 

 

 

使用方法:

XStream stream = new XStream();
stream.alias("h-cell", HCell.class);
stream.aliasAttribute(HCell.class, "width", "alias"); 
AttributeValueConveter converter = new AttributeValueConveter(stream.getMapper());  
converter.addConvertClass(PhoneNumber.class);  
stream.registerConverter(converter);
stream.registerConverter(new AttributeValueConveter(stream.getMapper()));

 

### 使用XStream自定义命名策略 为了满足将Java对象序列化为XML时,将类字段名转换为带有下划线分隔符的属性名称的需求,可以创建一个继承`com.thoughtworks.xstream.converters.ConversionException`包下的`com.thoughtworks.xstream.naming.NameCoder`接口或扩展默认实现`com.thoughtworks.xstream.naming.NoNameCoder`的新类来定制字段到XML标签映射规则。更简便的方法是利用XStream提供的`com.thoughtworks.xstream.XStream#useAttributeFor(Class type, String fieldName)`方法针对特定字段设置,但对于全局应用下划线风格,则推荐通过修改命名策略完成。 对于希望影响所有被序列化的类成员变量的方式,可以通过设定自定义的`NamingStrategy`实例给定XStream对象达成目的。下面展示了一个简单的例子说明怎样配置XStream以支持驼峰转下划线的功能: ```java import com.thoughtworks.xstream.XStream; import com.thoughtworks.xstream.converters.basic.AbstractSingleValueConverter; // 定义自己的命名策略 class UnderscoredNamingStrategy extends com.thoughtworks.xstream.mapper.MapperWrapper { public UnderscoredNamingStrategy(com.thoughtworks.xstream.mapper.Mapper wrapped) { super(wrapped); } @Override protected String aliasToSystemAttribute(String name) { return camelCaseToUnderscore(name); } private String camelCaseToUnderscore(String str){ StringBuilder result = new StringBuilder(); for (int i = 0; i < str.length(); ++i) { char ch = str.charAt(i); if(Character.isUpperCase(ch)){ if(i != 0)result.append('_'); result.append(Character.toLowerCase(ch)); }else{ result.append(ch); } } return result.toString(); } } public class Main { public static void main(String[] args) throws Exception { XStream xstream = new XStream(); // 设置自定义命名策略 xstream.setMapper(new UnderscoredNamingStrategy(xstream.getMapper())); User user = new User("JohnDoe"); System.out.println(xstream.toXML(user)); } static class User { private String userName; public User() {} public User(String userName) { this.userName = userName; } public String getUserName() { return userName; } public void setUserName(String userName) { this.userName = userName; } } } ``` 上述代码片段展示了如何构建一个新的`NamingStrategy`子类——`UnderscoredNamingStrategy`,该类负责处理从驼峰式命名法向使用下划线分割单词的形式转变的过程[^1]。接着,在初始化XStream实例之后立即将其应用于整个序列化进程之中。这样做的好处在于无需单独标注每一个需要改变形式的字段,而是统一按照既定规则进行调整。
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